1. Field of the Invention
The present invention relates to a power control apparatus for a four-wheel drive hybrid vehicle having an internal combustion engine and a motor as power sources.
2. Description of the Related Art
Conventionally, a power control apparatus for a hybrid vehicle is known in the art, which, for example, includes an internal combustion engine as a power source for driving front wheels, an AC generator that is driven by the internal combustion engine, an electrical energy storage device for storing electrical energy generated by the AC generator, and a motor that drives rear wheels by being supplied with electrical energy from the electrical energy storage device, and in which the amount of generation by the AC generator is controlled depending on the difference between the rotational speeds of the front wheels and the rear wheels (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 11-318001).
Moreover, conventionally, a hybrid vehicle is known in the art, which, for example, includes an internal combustion engine for driving either the front wheels or the rear wheels, a generator that is driven by the internal combustion engine, and a motor that drives the other of the front and rear wheels by being supplied with electrical energy from the generator, and in which a target torque of the motor is determined depending on the difference between the rotational speeds of the front wheels and the rear wheels, or depending on a depression amount of the accelerator pedal (see, for example, Japanese Unexamined Patent Application, First Publication No. 2001-177909).
In the above-mentioned power control apparatus for a hybrid vehicle, because the motor for the rear wheels is driven by merely being supplied with electrical energy from the electrical energy storage device, the capacity of the electrical energy storage device must be increased, or the output voltage of the electrical energy storage device must be made higher in order to increase the output power of the motor. In such a case, problems are encountered in that the electrical energy storage device becomes large, and high tension elements become large.
Moreover, in the above-mentioned hybrid vehicle, because the motor for driving either the front wheels or the rear wheels is driven by merely being supplied with electrical energy from the generator, the output power of the motor is limited by the maximum electrical power of the generator; therefore, a desired output power may not be obtained.